关于Kotlin data类
由于kotlin和java一样都是运行在jvm虚拟机上，所以最终生成的都是遵循jvm规范的字节码，因此可以通过反编译kotlin生成的字节码为java代码来学习kotlin的原理。
1.data类的写法
```
data class People(var name:String,var age:Int)
```
2.反编译成java代码后自动生成了变量的get、set方法，equals方法，copy方法，component1(),component2(),hashCode()方法,如下：
```
public final class People {
@NotNull
private String name;
private int age;
@NotNull
public final String getName() {
return this.name;
}
public final void setName(@NotNull String var1) {
Intrinsics.checkParameterIsNotNull(var1,"");
this.name = var1;
}
public final int getAge() {
return this.age;
}
public final void setAge(intvar1) {
this.age = var1;
}
public People(@NotNull String name, int age) {
Intrinsics.checkParameterIsNotNull(name,"name");
super();
this.name = name;
this.age = age;
}
@NotNull
public final String component1() {
return this.name;
}
public final int component2() {
return this.age;
}
@NotNull
public final People copy(@NotNull String name, int age) {
Intrinsics.checkParameterIsNotNull(name,"name");
return new People(name,age);
}
// $FF: synthetic method
// $FF: bridge method
@NotNull
public static People copy$default(People var0,String var1, int var2, int var3,Object var4) {
if((var3 &1) !=0) {
var1 = var0.name;
}
if((var3 &2) !=0) {
var2 = var0.age;
}
return var0.copy(var1,var2);
}
public String toString() {
return "People(name="+this.name +", age="+this.age +")";
}
public int hashCode() {
return (this.name !=null?this.name.hashCode():0) *31+this.age;
}
public boolean equals(Object var1) {
if(this!= var1) {
if(var1 instanceof People) {
People var2 = (People)var1;
if(Intrinsics.areEqual(this.name,var2.name) &&this.age == var2.age) {
return true;
}
}
return false;
}else{
return true;
}
}
}
```
3.如果变量是val修饰，如data class People(var name:String,val age:Int)，则只会为age变量生成get方法。
4.如果data类中需要定义常量，则常量的实际初始化阶段是在构造方法中，这点与java是不一样的
kotlin代码：
```
data class People(var name: String, var age: Int) {
val female=1
val male=2
}
```
反编译后的java代码（部分片段）：
```
private final int female;
private final int male;
@NotNull
private String name;
private int age;
public People(@NotNull String name, int age) {
super();
this.name = name;
this.age = age;
this.female =1;
this.male =2;
}
```
这点要尤其注意，因为在json的反序列化的过程中，如果调用的是无参构造方法（gson的实现），那么常量是没有进行过赋值的
